Antimicrobial Resistance in Six Priority Bacteria in Italy: Trends and Regional Variation, 2015-2024

Antimicrobial resistance (AMR) remains a major public health threat in Italy, where high incidence and mortality persist. In this study we aimed to describe national and regional trends in AMR rates from 2015 to 2024.

We conducted an ecological time-series analysis using publicly available data from the Italian AMR surveillance system (AR-ISS). We included six priority pathogens: methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE-faecium), third-generation cephalosporin-resistant Escherichia coli (3GCREC), carbapenem-resistant Klebsiella pneumoniae (CRKP), Pseudomonas aeruginosa (CRPA), and Acinetobacter spp. (CRAS). We analyzed annual resistance rates at national and regional level. Temporal trends were estimated using linear regression models, with calendar year as the independent variable. Regression coefficients, 95% CIs, and p-values were used to assess direction and significance. Relative percentage changes were calculated for 2015-2024 and, when relevant, for 2023-2024.

Resistance declined over time for four of six pathogens, but increased markedly for VRE-faecium, from 11.1% to 34.9%. Significant downward trends were observed for MRSA (β = -0.91, 95% CI: -1.35; -0.48, p = 0.0013), 3GCREC (β = -0.53, 95% CI: -0.99; -0.06, p = 0.0304), CRKP (β = -0.94, 95% CI: -1.35; -0.53, p = 0.0008), and CRPA (β = -0.86, 95% CI: -1.44; -0.27, p = 0.0095); VRE-faecium showed a strong upward trend (β = +2.76, 95% CI: 2.58; 2.94, p < 0.0001). CRAS remained consistently high throughout the study period. Considerable regional heterogeneity was observed across pathogens and geographical areas.

Despite progress for several pathogens, AMR remains a critical challenge in Italy. The persistent increase in VRE-faecium and the high burden of CRAS support the need for strengthened surveillance, stewardship, and region-specific infection prevention interventions.